The present invention relates to a bearing assembly and, more particularly, to an improved bearing assembly of a bottom bracket for a bicycle.
A conventional bottom bracket is shown in FIG. 1, which is disposed to the connecting point of the seat tube, down tube and the chain stay (figures not shown) to house rotatably cranks and pedals (figures not shown), the bottom bracket includes an axle 90, a tube 92, two caps 84 and a housing 80. The axle 90 having first and second ends is rotatably engaged within the tube 92 which has first and second ends and a threaded portion defined in an outer periphery of each of the first and second ends thereof for engagement with the housing 80. A threaded portion 902 is defined in an outer periphery of the first end of the axle 90, and the caps 84 are mounted on both ends of the housing 80 for keeping dust from entering therein. Two bearings 93, 94 are disposed between the axle 90 and the tube 92 to provide a better rotational efficiency. In order to maintain a position of the bearing 94, a race 95, a washer 962 and a nut 96 are threadedly mounted on the thread section 902 of the axle 90, the race 95 has an annular recess 952 defined in an outer periphery thereof and the tube 92 has a first annular recess 924 defined in an inner periphery of the first end thereof such that the bearing 94 is rotatably received therebetween. The axle 90 has an annular recess 91 defined in the outer periphery of the second end thereof and the tube 92 has a second annular recess 922 defined in the inner periphery of the second end thereof such that the bearing 93 is rotatably received therebetween.
However, as a bicycle often encounters rough and uneven terrain, especially for a mountain bike, the engagements of the bearings 93, 94 between the tube 92 and the axle 90 and the race 95 tends to become loose. Referring to FIG. 2, taking an engagement between the bearing 94, the race 95 and the tube 92 as an example, the engagement between the bearing 94 and the tube 92 has a first arc formed on an imaginary vertical plane (figure not shown) passing through a center O of the bearing 94, and the first arc has an upper distal point A and a lower distal point C. The engagement between the bearing 94 and the race 95 has a second arc formed on the imaginary vertical plane and the second arc has an upper distal point D and a lower distal point B. The points A and B are located on a vertical line L passing through the center O of the bearing 94, i.e., an angle between the vertical line L and the segment OA and OB are both equal to 0 degrees, such that when a force f is horizontally exerted to the bearing 94, the points A and B cannot dispense the force f, therefore, a stress concentration is occurred at the point C and D of the tube 92 and the race 95 respectively.
The present invention intends to provide an improved bearing assembly to mitigate and/or obviate the above-mentioned problems.